This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Vitamin B6 deficiency leads to a cellular deficiency of the coenzyme pyridoxal phosphate-PLP. PLP is a coenzyme in phases of one carbon-1C metabolism - the array in which one carbon units are used in reactions including nucleotide synthesis, regeneration of methionine- Met from homocysteine-Hcy, and methylation of many biological compounds. 1C metabolism is linked to the transsulfuration pathway in which Hcy undergoes PLP-dependent catabolism leading to cysteine. Nutritional or genetic conditions that impair 1C metabolism are associated with elevation in plasma Hcy concentration and increased risk of vascular disease. It is believed that the metabolic effects of vitamin B6 deficiency will be most pronounced following protein intake when the vitamin B6-dependent pathways of amino acid metabolism experience the greatest substrate load. Phase 1 will investigate the effects of vitamin B6 nutrition on the PLP-dependent generation of 1C units by the glycine cleavage system and on the synthesis of glutathione. Phase 2 will investigate the dependence of methionine metabolism on vitamin B6 nutritional status. Each phase will involve 14 young adults, who will undergo metabolite profiling and kinetic analysis using intravenously infused stable isotopic tracers performed before and after a ~4-week period of dietary vitamin B6 restriction. Subjects will be assigned to either Phase 1 or Phase 2, which will be identical in design except for the tracers and analytical methods used. We hypothesize that vitamin B6 deficiency will yield reduction in postprandial rates of homocysteine remethylation, generation of 1C units from glycine, and synthesis of glutathione.